Aqueous must flow circumferentially in Schlemm's canal from its entry into the canal at an endothelial pore to its exit from the canal at a collector channel. The canal offers resistance to circumferential flow, and therefore to outflow, which becomes greater as the canal becomes narrower. It is this resistance to outflow with resultant build-up of intraocular pressure which may be an important element in the cause of glaucoma. We will measure the width of the canal of Schlemm and its contribution to resistance to outflow in enucleated human eyes by perfusion of the canal with contrast media or saline while the pressure gradient from anterior chamber to episclera is maintained at known levels. Pressure gradient will be maintained by embedding the eye in porous medium through which suction is applied while allowing access to Schlemm's canal and anterior chamber. The project is designed to assess the canal of Schlemm as a site of resistance to aqueous outflow and to clarify its role in the development of glaucoma. The magnitude of canal resistance as a function of intraocular pressure will be measured.